Shoring structure

ABSTRACT

Disclosed herein are shoring structures having bases and telescoping members, each shoring structure being fabricated of square tubing. In one embodiment of the structure, square tubing of the telescoping member telescopes inside and along square tubing of the base. In a second embodiment, square tubing of the telescoping member telescopes outside and along square tubing of the base member. In yet another embodiment both inner and outer square tubing of the telescoping member telescopes along square tubing of the base. Lock means are associated with the bases and telescoping members to lock thereto cross bracing between base members, telescoping members, etc. Such lock means include a slidable member which is slidable to a position holding the end portion of a cross brace, and to a position freeing the end portion of the cross brace.

United States Patent 1 Ballou [451 May 1, 1973 SHORING STRUCTURE [76]Inventor: Clayton R. Ballou, 136 Baltrusal Place, San Ramon, Calif.

[22] Filed: May 20, 1971 [21] Appl. No.: 145,980

Related [1.8. Application Data [62] Division of Ser. No. 846,759, Aug.1, 1969, Pat. No.

[52] US. Cl ..287/53.5 [51 Int. Cl ..E04g 7/22 [58] Field of Search..287/53.5

[56] References Cited UNITED STATES PATENTS Moritz 287/535 Albrecht eta1 ..287/53.5

Primary Examiner-Andrew V. Kundrat Att0rney-Mellin, Hursh, Moore &Weissenberger [5 7] ABSTRACT Disclosed herein are shoring structureshaving bases and telescoping members, each shoring structure beingfabricated of square tubing. In one embodiment of the structure, squaretubing of the telescoping member telescopes inside and along squaretubing of the base. In a second embodiment, square tubing of thetelescoping member telescopes outside and along square tubing of thebase member. In yet another embodiment both inner and outer squaretubing of the telescoping member telescopes along square tubing of thebase.

Lock means are associated with the bases and telescoping members to lockthereto cross bracing between base members, telescoping members, etc.Such lock means include a slidable member which is slidable to aposition holding the end portion of a cross brace, and to a positionfreeing the end portion of the cross brace.

3 Claims, 21 Drawing Figures PATENTED RAY H375 SHEET 2 OF 5 FlG 2 FIG 4snonmc STRUCTURE CROSS REFERENCE TO RELATED APPLICATION BACKGROUND OFTHE INVENTION This invention relates to shoring structures and, moreparticularly, to such a shoring structure which utilizes a telescopingmember which may be set at a variety of heights.

In the shoring of, for example, overpass roads which are being built, itis well known to provide a series of shoring structures, each having alower base, and a telescoping upper frame member which may be set at oneof a variety of heights, depending on the height of the load to beshored. Generally, the common shoring structure is fabricated of tubingof round cross-section, and the upper frame member has a pair ofparallel tubular legs which are slidably positioned within a pair ofparallel tubular legs which comprise part of the base. Means areincluded to selectively set the telescoping member at its proper height.

Because of the uses of such shoring structures, it is, of course,extremely important that it be quite strong, and so improvements in thisdirection are constantly being sought. An especially critical area isthe telescoping member itself, and its interconnection with the basemember. While the structure overall should be extremely strong, itshould be designed so that telescoping can be easily and convenientlyachieved. Above and beyond this, each overall shoring structure shouldbe as simple and easy to use as possible.

As stated previously, a series of shoring structures of the typedescribed are often used. In such circumstance, brace membersinterconnect the shoring structures, so that the overall resultingstructure is strong and stable. The ends of these brace members shouldbe properly fixed to the shoring structures by convenient means toprovide proper bracing, but should be easily and conveniently removabletherefrom so that the shoring may be taken down quickly and easily whenno longer needed.

Finally, when it is necessary for the shoring structure to be built upto a relatively great height, means should be provided to allow bases tobe stacked one on top of the other in a safe, strong and convenientmanner. On top of these may then be placed a telescoping member, toprovide the close adjustment in height previously described.

It is therefore an object of this invention to provide a shoringstructure which (i) includes a telescoping member which can be easilyand conveniently adjusted, and (ii) is of such overall design as to haveextremely great load-bearing qualities.

It is a further object of this invention to provide means for securinginterconnecting brace members to a pair of shoring structures by meanswhich securely hold the brace members when required, yet can easily bemanipulated to allow the brace members to be easily and convenientlyremoved. 7

It is a still further object of this invention to provide means whichallow bases to be stacked one on top of the other in a safe, strong andconvenient manner.

SUMMARY OF THE INVENTION Broadly stated, the inventive shoring structurecomprises a base having a pair of generally parallel, tubular legs ofsquare cross section, with cross bracing of square cross sections and atelescopic frame member having a pair of generally parallel, tubularlegs of square cross-section slidable along the legs of the base, eitherinside or outside thereof, so that the telescopic frame member isslidable inwardly and outwardly of the base. Each leg of the telescopicframe member has a plurality of spaced apertures therethrough. Furtherincluded are first and second pins, the first pin being positionable inany one of the apertures in one leg of the frame member, the second pinbeing positionable in the corresponding apertureof the other leg of theframe member. Means are associated with the legs of the base to limitthe inward sliding of the frame member relative to the base by blockingthe pins positioned in their respective apertures.

This invention further comprises a lock for securing the end portion ofa longitudinal cross member relative to a frame portion. Such lockcomprises a support member fixed to the frame portion, and a shaft fixedto and extending from the support member, the end portion of thelongitudinal member being positionable so that the shaft is disposedthrough an aperture through said end portion of the longitudinal member.A slidable member is' associated with the support member and slidablerelative thereto. An arm is fixed to and extends from the slidablemember, the slidable member being slidable to a first position where theend of the arm is removed from the shaft to freely allow the end portionof the longitudinal member to be positioned so that the shaft isdisposed through the aperture, and to freely allow removal of theportion of the longitudinal member from such position, the slidablemember being slidable to a second position where the end of the arm isadjacent the shaft, so that the movement of the portion of thelongitudinal members from said position with the shaft disposed throughthe aperture is limited by the arm.

This invention further comprises a frame structure, comprising a firstlongitudinal upright tube of generally square cross section, and asecond longitudinal upright tube of generally square cross section abovethe first tube and aligned therewith, and having its lower endpositioned adjacent the upper end of the first tube. A rigid connectingbar defines an upper portion disposed in the lower end of the secondtube, a lower portion of the connecting bar disposed in the upper end ofthe first tube, and a circumferential lip thereabout intermediate theupper and lower portions of said connecting bar, which rests on theupper end of the first tube, and on'which rests the lower end of thesecond tube.

BRIEF DESCRIPTION OF THE DRAWINGS These and other objects of theinvention will become apparent from a study of the followingspecification and drawings, in which:

FIG. I is an overall perspective view of a pair of base shoringstructures interconnected by brace members in accordance with theinvention;

FIG. 2 is a front elevation of a shoring structure of FIG. 1 with afirst embodiment of telescoping frame member;

FIG. 3 is a view taken along the line 3 3 of FIG. 2, with a portionbroken away;

FIG. 4 isa sectional view taken along the line 4-4 of FIG. 3;

FIG. 5 is a view similar to that of FIG. 2, but with a second embodimentof telescoping frame member;

FIG. 6 is a view taken along the line 6-6 of FIG. 5, with a portionbroken away;

FIG. 7 is a view taken along the line 77 of FIG. 6, with portionsremoved;

FIG. 8 is a sectional view taken along the line 88 of FIG. 6;

FIG. 9 is a view similar to that of FIGS. 2 and 5, but with a thirdembodiment of telescoping frame member, and with a portion of the baseremoved;

FIG. 10 is a front elevation of a leg of the telescoping frame member ofFIG. 9 partially broken away, and with a portion removed;

FIG. 1 l is a side elevation of the leg of FIG. 10;

FIG. 12 is a sectional view taken along the line 12- 12 of FIG. 10;

FIG. 13 is a sectional view taken along the line 13- FIG. 14 is asectional view taken along the line 14- 14 of FIG. 11, rotated 90;

FIG. 15 is a front elevation of a pair of bases, one stacked on theother;

FIG. 16 is a view taken along the line l6 l6 of FIG. 15, with portionsbroken away;

FIG. 17 is a sectional view taken along the line 17- 17 of FIG. 16;

FIG. 18 is a perspective view of the lock as used in FIG. 1 to lock thecross brace members to a series of bases;

FIG. 19 is a side elevation of the lock of FIG. 18;

FIG. 20 is a front elevation of the lock of FIGS. 18 and 19;

FIG. 21 is a plan view of the lock of FIGS. 18-20.

DESCRIPTION OF THE PREFERRED EMBODIMENT Shown generally in FIG. I is ashoring system 10 made up ofa pair of shoring structures l2, l4interconnected by longitudinal cross brace members 16, 18, 20, 22. Eachshoring structure, such as shoring structure 12, is made up of a base24, and a telescoping frame member 26. Such a shoring structure 12 isshown in detail in FIGS. 2-4.

As shown therein, base 24 has a pair of generally parallel legs 28,which are interconnected by cross members 32, 34, 36, 38, so as to berigidly positioned relative to each other. Above the base 24 is atelescopic frame member 40, which also has a pair of generally parallellegs 42, 44 which are interconnected and reinforced by braces 43A, B, Cand D. The legs 28, 30, 42, 44 are each square in cross section, as arebraces 43A, B, C and D, and are actually tubular in configuration. Thecross sections of legs 42, 44 are such that the legs 42, 44 arepositionable within the inner bores of the tubular legs 28, 30. Thepositioning ofleg 44 within inner.

bore 30A of leg 30 is shown in FIGS. 3 and.4, it being. understood thatlegs 28, 42 cooperate in the same manner. A certain amount of' clearanceis provided between legs 42, 44 and the inner bores of legs 28, 30respectively, so that the legs 42, 44 are slidable insidev and along thelegs 28, 30. Thus the telescopic frame member 40 is slidable inwardlyand outwardly of the base 24.

therethrough, and leg 44 has a corresponding plurality of spacedapertures 48 therethrough. Each of the apertures 46, 48 is square incross-section. A pair of blocking members 50, 52 are positioned on thetop ends 29, 31 of legs 28, 30 of base member 24. One such blockingmember 52 is shown in detail in FIGS. 3 and 4. As shown therein,blocking member 52 has a downwardly extending edge 54 which surroundsthe top end 31 of leg 30, and has an aperture 55 therethrough allowingfree sliding of leg 44 therethrough. A pin 56 of square cross-section ispositionable in any of the apertures 48 through leg 44, and, as leg 44is lowered, a flat side 56A of pin 56 will bear against blocking member52, sitting in a flat recess 58 provided therefor, so as to limit theinward sliding of leg 44 relative to leg 30.

A similar pin 60 of square cross-section is positionable in any of theapertures 46 through leg 42, and cooperates with blocking member 50 in asimilar manner. In this way, the inward sliding of the telescopic framemember 40 relative to the base 24 may be limited with the telescopicframe member 40 at a desired height.

A second embodiment of telescopic frame member 70, associated with abase 24 as previously described, is shown in FIGS. 5-8. As showntherein, telescopic frame member has a pair of generally parallel legs72, 74 of square cross-section which are interconnected and reinforcedby bracing 73A, B, C and D of square cross-sections. Leg 74 and itsassociation with leg 30 of base 24 are shown in detail in FIGS. 6-8. Asshown therein, leg 74 defines an inner bore 74A, and leg 30 of base 24is positioned within that inner bore 74A, with a small clearancetherebetween. In this way, leg 74 is slidable outside and along leg 30of the base 24, with a longitudinal gap 76 being provided in leg 74 toallow clearance for the ends of cross members 32, 34, 36, 38 of base 24.It will be understood, of course, that leg 72 is associated with leg 28in a similar manner.

Leg 74 has a plurality of spaced apertures therethrough, and leg 72 hasa plurality of spaced apertures 78 therethrough. Each of the apertures78, 80 is square in cross section, as shown.

A pin 82 of square cross-section is positionable in any of the apertures80, and a flat surface 82A thereof will bear on the flat top end 31ofleg 30, so as to limit the inward sliding of leg 74 relative to leg30. A similar pin is positionable in any of the apertures 78, andcooperates with the top end 29 of leg 28 in a similar manner. In thisway, the inward sliding of telescopic frame member 70 relative to base24 may be limited, with the telescopic frame member 70 held at a desiredheight.

A variation of telescopic frame member 70 is shown in FIGS. 9-14. Asshown therein, a telescopic frame member has tubular legs 92, 94 ofsquare cross section which are interconnected and reinforced by bracing93A, B, C and D of square cross-section. Legs 92, 94 are slidableoutside the legs 28, 30 of a base 24, similar to telescopic frame member70. As shown in detail in-FIGS. 10-14, leg 92 has a spacer 96, of squarecross section welded therewithin adjacent the top end thereof, and atubular guide 98, of square cross section, has its top end welded withinthe spacer 96. Guide 98 is thus spaced from the inner bore 100 of leg92. Guide 98 extends downwardly below the bottom end of leg 92. Incooperation with the leg 28 of base 24, guide 98 is disposed within theinner bore 28A of leg 28, with the leg 28 itself within the inner bore100 of leg 92. Leg 94 also includes a guide 102 associated therewith,which cooperates with leg 30 in a similar manner. Spaced apertures 104of square cross-section are provided through leg 92, and spacedapertures 106 of square cross-section are provided through leg 94.Guides 98, 102 define spaced apertures 108, 110 of square crosssectionwhich cooperate with apertures 104, 106, so that pins of squarecross-section, such as pin 112, can be disposed therethrough, and willrest with flat surfaces thereof flush against the flat top ends 29, 31of legs 28, 30 to limit the inward telescoping of telescopic framemember 90.

The shoring structures as disclosed may be set at a variety of heights,and may be used in a series in cooperation with jack means (not shown)if they are on uneven ground, as is well known. I

The particular advantages of these designs should be noted. First, sinceeach embodiment is fabricated of square tubing, it is extremely strong.Each embodiment is also quite easy to manufacture, when compared withshoring of round tubing. When using round tubing, each end ofacross-tube must be particularly cove cut to mate with the roundedsurface of the tube to which it is to be joined, or each end must besmashed to flatten it out so that it can be welded. The former isobviously disadvantageous, as it is quite time-consuming, and the latterhas been found to create cracks in the metal that can result in failureafter welding, if the ends are smashed when cold. Heating the endsbefore smashing is expensive and time-consuming, and is generally notdone.

In fabricating a shoring structure of tubing of square cross section,only one straight cut need be made on each end of a cross tube, so thatit will mate with the flat surface of the tube of square cross-sectionto which it is to be joined. Also adding to the strength of thestructure is the fact that no holes need be punched in the base of anyembodiment.

In addition, the load-supporting pins are square in cross-section, andset in square apertures, with flat surfaces thereof engaging with flatbearing surfaces. Because of this design, the load on the telescopicframe member is distributed over a flat area, ensuring that the shearload capacity of the pin is very high. As a comparison, if the pin wereround, the loaded area would be smaller, and in fact could well be asingle point if the pin is disposed in a slightly oversize roundaperture. In such case, many failures occurred because of the splittingof the tubing by this single point contact.

In any of the embodiments, it will be seen, telescoping of the framemember, and then setting it at its chosen height can be easily andconveniently achieved,

merely by removing the pins, sliding the frame member, and reinsertingthe pins in the chosen apertures.

In particular, the blocking members 50, 52 of the first-describedembodiment spread the load over the whole area of the top ends 29, 31 ofthe legs 28, 30, providing even greater load-bearing qualities.

The provision of guides tubes 98, 102 as shown in the third-describedembodiment (FIGS. 10-14), provided a number of advantages. First,because of the double tube design of each leg, even greater strength isprovided. Second, the load on each pin is spread over an even greaterarea, that is, that defined by apertures both in the leg and in theguide associated therewith. Third, the double tube structure, whencooperating with a leg of base 24, provides a rigidity betweentelescopic top frame member and base which does away with any need forconnecting braces between the telescopic top frame member and base.Although the tubes of FIGS. 6 14 are shown as square in cross-section,the telescoping member may be adapted to a standard base having tubularlegs of circular cross-section.

Shown in FIGS. 15-17 are means for stacking bases 24, 24 on top of eachother to achieve greater overall shoring height. Such means are used incooperation with upright tubes of square cross section, such as the legs28, 28 and legs 30, 30 of bases 24, 24. Such means comprise a rigid bar120, as shown associated with tubular legs 30, 30', it being understoodthat a like bar is associated in a similar manner with tubular legs28,28.

The rigid bar 120 defines an upper portion 122 which in turn definesfour longitudinal ribs 124, 126, 128, 130, a lower portion 132 definingfour similar ribs, and a circumferential lip 134 intermediate the upperand lower portions 122, 132. As shown, the ribs 124, 126, 128, 130defined by the upper portion 122, and the corresponding ribs defined bythe lower portion 132, taper inwardly away from the circumferential lip134. In use, the lower portion 132 of the bar 120 is disposed in theupper end of the leg 30 and the upper portion 122 of the bar 120 isdisposed in the lower end of the leg 30, with the circumferential lip134 resting on the end 31 of leg 30, and on which rests the lower end.33 of leg 30. In such use, the ribs 124, 126, 128, 130 are positioned inthe inner corners 136, 138, 140, 142 defined by the lower end of thesquare-tube leg 30'. Similarly, the ribs defined by lower portion 132are positioned in the inner corners defined by the upper end ofsquare-tube leg 30. It will be seen that such design allows bases to bestacked on one another in series in a very strong, stable manner. Thisis so because of the ribs which are positioned in the inner cornersdefined by the legs. The taper of these ribs ensures that there can beno binding between the upper and lower portions of the rigid bar and thelower and upper ends of the legs.

As stated previously, FIG. 1 shows a pair of shorting structures 12, 14interconnected by brace members l6,-

18, 20, 22. Locks 200, fixed to the legs of the bases of shoringstructures l2, 14, are used to secure the end portions of thelongitudinal brace members 16, 18, 20, 22 to the legs of the bases. Oneof such locks 200, in cooperation with leg 30 of base 24, is shown indetail in FIGS. 18-21. Such lock 200 comprises a channel support member202 fixed to leg 30 and defining an opening 204 therethrough. A shaft206 is fixed to and extends from the support member 202. A slidablemember 208 is disposed through the opening 204 defined by the supportmember and is slidable relative thereto.

The slidable member'208 has arms 210, 212 fixed to and extendingoutwardly and toward each other from the ends thereof.

The slidable member is slidable to a first position (shown in full inFIG. 19) where the ends 214, 216 of arms 210, 212 are removed from theshaft 206 When in such first position, the flattened end portion 22A ofthe longitudinal cross member 22 may be.positioned so that the shaft 206is disposed through an aperture 218 in the end portion 22A, and may befreely removed from such position. The slidable member 208 is alsoslidable to a second position (FIG. 18) where a portion 220 of the arm210 adjacent the end 214 is positioned in a slot 222 in the shaft 206,so that the arm 210 extends from one side 224 of the shaft 206 to theother side 226, with the end 214 extending from the other side 226. Insuch second position, a nail or cotter pin 228 may be positioned throughan opening 230 in the end 214 of the arm 210, to limit the movement ofthe end 214 of the arm 210 from its position on the other side 226 ofthe shaft 206. The slidable member 208 may thus be selectively held inits second position, whereby the end portion 22A of the longitudinalmember 22 is locked on the shaft 206 by arm 210. Stop means 232 areincluded at one end of the slidable member 208 to contact the supportmember 202 to limit the sliding of the slidable member 208 in thatdirection, to define the second position of the slidable member.

The slidable member 208 is also slidable to a third position (shown inphantom in FIG. 19) where a portion 240 of the arm 212 is positioned inslot 222, so that the arm 212 extends from the other side 226 of theshaft 206 to the one side 224, with the end 216 extending from the oneside 224. In such third position a nail or cotter pin, similar to cotterpin 228, may be positioned through an opening 242 in the end 218 of arm212, to hold the arm 212 in such position, locking the end portion 22Aof the brace member 22 on shaft 206.

Similar to stop means 232, stop means 244 are included at the other endof the slidable member 208 to contact the support member 202 to limitthe sliding of the slidable member 208 in that direction, to define thethird position of the slidable member 208.

The base 222A of the slot 222 may be chamfered so that the arms 210, 212are raised to an extent as they are seated in slot 222. This providesacertain amount of springing in the arms 210, 212, aiding in the lockingaction of the lock 200.

Such locks 200 as disclosed, where used throughout a shoring system suchas that shown at 10 in FIG. 1, ensure a positive locking means forsecuring cross braces to the legs of the bases. The locks 200, it willalso be seen, can be easily used to selectively lock or unlock suchbrace members, so-that the overall shoring system may be built up,changed, or disassembled easily and conveniently.

'Ic'laim:

1. A lock for securing a portion of a longitudinal member relative to aframe portion comprising:

, a. a support member fixed to the frame portionj b. a shaft fixed toand extending from the support member, the portion of the longitudinalmember being positionable so that the shaft is disposed through anaperture through said portion of the longitudinal member;

member and slidable relative thereto;

d. an arm fixed to and extending from the slidable member, the slidablemember being slidable to a first position where the end of the arm isremoved from the shaft to freely allow said portion of the longitudinalmember to be positioned so that the shaft is disposed through theaperture,.and to freely allow removal of said portion of thelongitudinal member from such position, the slidable member beingslidable to a second position where the end of the arm is adjacent theshaft, so that the movementof the portion of the longitudinal memberfrom said position with the shaft disposed through the aperture islimited by the arm, a portion of the arm adjacent the end thereof beingpositioned in a slot in the shaft so that the arm extends from one sideof the shaft to the other, with the end of the arm extending from saidother side of the shaft, when the slidable member is in its secondposition, means selectively positionable through an opening in the endof the arm when it extends from said other side of the shaft, to limitthe movement of the end of the arm from its position on said other sideof the shaft, whereby the slidable member may be selectively-held in itssecond position, and

a second arm fixed to and extending from the slidable member, thefirst-mentioned and second arms being on opposite sides of the supportmember, the end of the second arm being removed from the shaft when theslidable member is in its first position to freely allow the portion ofthe longitudinal member to be positioned so that the shaft is disposedthrough the aperture, and to freely allow removal of said portion of thelongitudinal member from such position, the slidable member beingslidable to a third position where the end of the second arm is adjacentthe shaft, so that the movement of the portion of the longitudinalmember from said position with the shaft disposed through the apertureis limited by the second arm, a portion of the second arm adjacent theend being positioned in the slot in the shaft, so that the second armextends from said other side of the shaft to said one side of the shaft,with that end-of the arm extending from said one side of the shaft, whenthe slidable member is in its third position.

2. A lock according to claim l wherein are included means selectivelypositionable through an opening in the end of the second arm when itextends from said one side of the shaft, to limit the movement of theend of the second arm from its position on said one side of the shaft,whereby the slidable member may be selectively held in its thirdposition.

3. A lock according to claim 1 wherein are further included first andsecond stop means associated with the slidable member to contact thesupport member to limit the movement of the slidablesmember and definethe second and third positions thereof respectively.

1. A lock for securing a portion of a longitudinal member relative to aframe portion comprising: a. a support member fixed to the frameportion; b. a shaft fixed to and extending from the support member, Theportion of the longitudinal member being positionable so that the shaftis disposed through an aperture through said portion of the longitudinalmember; c. a slidable member associated with the support member andslidable relative thereto; d. an arm fixed to and extending from theslidable member, the slidable member being slidable to a first positionwhere the end of the arm is removed from the shaft to freely allow saidportion of the longitudinal member to be positioned so that the shaft isdisposed through the aperture, and to freely allow removal of saidportion of the longitudinal member from such position, the slidablemember being slidable to a second position where the end of the arm isadjacent the shaft, so that the movement of the portion of thelongitudinal member from said position with the shaft disposed throughthe aperture is limited by the arm, a portion of the arm adjacent theend thereof being positioned in a slot in the shaft so that the armextends from one side of the shaft to the other, with the end of the armextending from said other side of the shaft, when the slidable member isin its second position, means selectively positionable through anopening in the end of the arm when it extends from said other side ofthe shaft, to limit the movement of the end of the arm from its positionon said other side of the shaft, whereby the slidable member may beselectively held in its second position, and a second arm fixed to andextending from the slidable member, the first-mentioned and second armsbeing on opposite sides of the support member, the end of the second armbeing removed from the shaft when the slidable member is in its firstposition to freely allow the portion of the longitudinal member to bepositioned so that the shaft is disposed through the aperture, and tofreely allow removal of said portion of the longitudinal member fromsuch position, the slidable member being slidable to a third positionwhere the end of the second arm is adjacent the shaft, so that themovement of the portion of the longitudinal member from said positionwith the shaft disposed through the aperture is limited by the secondarm, a portion of the second arm adjacent the end being positioned inthe slot in the shaft, so that the second arm extends from said otherside of the shaft to said one side of the shaft, with that end of thearm extending from said one side of the shaft, when the slidable memberis in its third position.
 2. A lock according to claim 1 wherein areincluded means selectively positionable through an opening in the end ofthe second arm when it extends from said one side of the shaft, to limitthe movement of the end of the second arm from its position on said oneside of the shaft, whereby the slidable member may be selectively heldin its third position.
 3. A lock according to claim 1 wherein arefurther included first and second stop means associated with theslidable member to contact the support member to limit the movement ofthe slidable member and define the second and third positions thereofrespectively.